The comedian took to Twitter to express her condolences, saying, "This year I met a very special girl, and today we lost her. Sending my heart to Talia's family."

"I'm so sad," she added.

Talia was a guest on "The Ellen DeGeneres Show" to address her brave battle with neuroblastoma for over six years. She also explained to the TV host that she was recently diagnosed with pre-leukemia.

The charismatic teen got her first taste of fame after inspiring hundreds of thousands of people with her makeup tutorials on YouTube. In fact, the youngster garnered over 15 million views on her candid clips alone.

Ellen, who is currently a representative of CoverGirl, surprised the beauty maven with her very own beauty advertisement from the brand.

"CoverGirl heard your story and they want to make you an honorary CoverGirl," Ellen explained.

"I am inspired by people like yourself. I think there are a lot of people who go through a lot of struggling situations and despite what the doctors have said and the cancer you're going through, how do you stay so positive?" she asked.

"When people ask me that, what do you want me to do, be depressed? I mean a little fishy [Dory of "Finding Nemo," voiced by DeGeneres] told me, 'Just keep swimming, just keep swimming!'" Talia responded.

"You are really quite something. There's a depth to your soul that is not a 13-year-old soul," Ellen said. "You're an old soul and you are very special and amazing and I'm so honored that you wanted to meet me and that I got to meet you."

Talia's Facebook account was updated with a picture of her in a white sweat suit with an emotional goodbye message to the star.

"#prayfortalia It is with a heavy heart that we share with all of you that Talia has earned her wings at 11:22am. Please lift her beautiful soul, her beautiful light to heaven and please send your love and prayers to her family during this most difficult time."

The post went on to say, "We will miss you more than you will ever know baby girl."

CoverGirl paid tribute to Talia by tweeting the following message, "Talia Castellano was the meaning of a true COVERGIRL. Please join me in sending love and honoring her memory."